How should I handle unused pins?

Question:

How should I handle unused pins?

Answer:

Input pins These pins cannot be left open. Connect input pins to the power supply or ground. (except when these pins are pulled up or down internally)

Output pins These pins can be open. However, we recommend connecting open-drain output pins to the same electric potential line (power supply or ground) as potential of the pins whose transistor is in the ON to protect against damage due to static electricity.

I/O pins (data bus, address bus, I/O ports, etc.) The handling differs depending on the function. Set the pins in the output mode whenever possible. In this case, these pins can be handled in the same way as output pins. If the pins may become input pins, pull them up (or down) using an appropriate resistor for each.

The pin processing procedures of some of the RF/microwave/display devices differ from one another. For details, consult your nearest distributor. Regarding photocouplers having many channels, however, all the pins of the unused channel should be grounded to make their potential the same, or left open.